Termination or connection of high or medium voltage electrical cables in the field requires electrical shielding or stress control. Geometric electrical stress control and/or shielding of elastomeric cable accessories may be generally accomplished by one of the two following methods.
In one method, an elastomeric semiconductive geometric stress control insert is pre-molded in one manufacturing operation. The insert is subsequently bonded to an elastomeric insulating dielectric in a second molding operation. This method has certain disadvantages. The pre-molded semiconductive components are nominally 0.020 inches thick or thicker. The component, therefore, must be trimmed of flash and cleaned. Also, the components must be specially stored to accommodate the secondary molding and bonding process. The thicker pre-molded semiconductive components may impart undesirable physical characteristics to the final product. These characteristics include higher modulus, resulting in a stiffer final product. This is especially significant in the wide range of cable accessory designs where the product is radially expanded significantly and the modulus must be controlled.
Another method includes molding the elastomeric insulating dielectric by one process and applying a semiconductive coating in a second process. This semiconductive coating may be applied by conventional techniques such as brushing, dipping, or spraying. This technique also has certain disadvantages. The application of the secondary coating to irregular interior surfaces is very difficult to achieve effectively and is costly to apply. Chemical cross-linking (chemical bonding) between an elastomeric semiconductive coating and an elastomeric insulating dielectric cannot be satisfactorily achieved unless the coating is subsequently cured or vulcanized by using heat and/or pressure during a secondary operation. The shelf life of these components is limited in that the coatings are reactive systems containing catalysts.
It is therefore desirable to provide a coating and application process for an elastomeric electrical cable accessory which is more reliable and cost-effective to achieve.